1. Field of the Invention
The present invention relates to a transflective liquid crystal display having features of both reflective and transmissive displays and a method for manufacturing the transflective liquid crystal display.
2. Description of the Related Art
In general, transmissive liquid crystal displays using backlights for displaying images have been mainly used as displays for personal computers. Recently, however, there have been increasing demands for displays for mobile electronic devices such as personal digital assistants (PDAs) and mobile phones, and reflective liquid-crystal displays which consume less power than the transmissive liquid crystal displays have been attracting attention. In the reflective liquid crystal displays, ambient light incident on and reflected by a reflector is used for displaying images, so no backlight is necessary and power consumption is low. Therefore, electronic devices including the reflective liquid crystal displays can be operated for a longer time compared to those including the transmissive liquid crystal displays.
For the case in which the reflective liquid crystal displays, which normally use ambient light for displaying images, are used in dark places, a construction has been proposed in which a front light is arranged on a display side, that is, on the front of a liquid crystal panel and light emitted from the front light is used for displaying images. However, when the front light is disposed on the display side of the panel, the reflectivity and the contrast decrease and the image quality degrades.
In order to solve this problem, transflective liquid crystal displays in which a reflector has a transmissive area in a pixel area and which have features of both the reflective and transmissive liquid crystal displays have been developed. In the transflective liquid crystal displays, a backlight is arranged on a liquid crystal panel on the side opposite to the display side, so that sufficient visibility can be obtained in both dark and light places without degrading the image quality as a reflective display. Accordingly, high image quality can be obtained. The basic construction of the transflective liquid crystal displays is disclosed in, for example, Japanese Unexamined Patent Application Publications Nos. 2000-29010 and 2000-35570.
With reference to FIG. 27, in a known transflective liquid crystal display 101, a reflective electrode 104 composed of a material with high reflectivity and a transparent electrode 105 composed of a material with high transmittance are provided on a main surface of a substrate 102, the reflective electrode 104 being laminated on the substrate 102 with an interlayer film 103 therebetween, and a quarter-wavelength layer (hereinafter called a λ/4 layer) 106 and a polarizer 107 are laminated on the other main surface of the substrate 102 in that order. In addition, in the liquid crystal display 101, a counter electrode 109 is provided on a main surface of another substrate 108 on the side facing the substrate 102, and a λ/4 layer 110 and a polarizer 111 are laminated on the other main surface of the substrate 108 in that order. A liquid crystal layer 112 composed of a liquid crystal material is interposed between the reflective electrode 104 and the counter electrode 109 and between the transparent electrode 105 and the counter electrode 109. Thus, the liquid crystal display 101 shown in FIG. 27 includes two retardation layers, one on the front and one on the back.
In order to reliably suppress the influence of chromatic dispersion and improve the dark state display, the construction shown in FIG. 28 may also be used. In a liquid crystal display 201 shown in FIG. 28, a λ/4 layer 106 and a half-wavelength layer (hereinafter called a λ/2 layer) 113 provided on a substrate 102 are used in combination with each other and a λ/4 layer 110 and a λ/2 layer 114 provided on a substrate 108 are used in combination with each other. Thus, four retardation layers are used in total.
In the liquid crystal display 101 shown in FIG. 27, the λ/4 layer 110 which serves as a retardation layer is provided on the display side of the substrate 108 such that it covers the entire area of the substrate 108 in order to suppress the influence of chromatic dispersion and achieve reflective display. Therefore, although a retardation layer such as a λ/4 layer is not necessary for transmissive display, since the λ/4 layer 110 which is provided on the display side for achieving reflective display covers the entire area of the substrate 108, the λ/4 layer 106 must be provided on the substrate 102 arranged on the back in order to compensate for the phase difference of the λ/4 layer 110. More specifically, since a retardation layer is provided on the display side for achieving reflective display even though it is not necessary for transmissive display, an additional retardation layer must be provided to compensate for the phase difference of the retardation layer arranged on the display side.
Similarly, in the liquid crystal display 201 shown in FIG. 28, two of the four retardation layers which are placed on the back are simply provided to compensate for the phase difference of the other two retardation layers used for reflective display, and are not necessary for transmissive display.
As described above, in known transflective liquid crystal displays, the required number of retardation layers is large compared to the reflective liquid crystal displays and the transmissive liquid crystal displays. Accordingly, high costs are incurred and the cell thickness is large.